One proposed benefit of vitamin D supplements is to help prevent age-related loss of muscle power and function (especially in the legs), which contributes to the risk of falls and fractures in older people. But some research has raised doubts about this, including a well-designed clinical trial from Tufts University published in the American Journal of Clinical Nutrition in March 2019.
There is a theoretical basis for the proposed benefit, because of the vitamin’s role in muscle cells. In addition, observational studies have found that older people with low blood levels of vitamin D tend to have worse leg muscle function, though vitamin D status may merely be a marker for better health and more time spent outdoors in the sun (sunlight causes the skin to make the vitamin). As we have previously reported, placebo-controlled clinical trials testing vitamin D supplements (with or without calcium supplements) for muscle function and fall prevention have had mixed results.
And while the U.S. Preventive Services Task Force in 2012 advised D supplements for people over 65 in order to prevent falls related to muscle weakness, in 2018 it reversed itself and recommended against such supplementation except for people with known vitamin D deficiency, in light of an updated research review.
The Tufts researchers hypothesized that vitamin D would indeed be beneficial for muscles of older people, based on their previous research. Their study involved 100 healthy people, average age 70, who initially had relatively low blood levels of D (averaging 20 ng/mL); half were given 800 IU of the vitamin a day (which is the daily RDA for people ages 70 and older); the other half a placebo. After four months, blood levels of participants in the D group were measured, and those who still had relatively low levels were given an additional 800 IU a day.
After a total of one year, average blood levels of D in the treatment group rose to 32 ng/mL (many experts advise levels over 30, though the National Academy of Sciences has set the cutoff at 20 for bone health). Testing of the participants showed no differences in leg muscle strength or function between the two groups, or in the number of falls.
It’s possible that vitamin D might have been beneficial if the participants had been frailer or had lower initial D levels, or if higher doses of D had been used for longer than a year, the authors suggested.
Harvard researchers are continuing to analyze data from the important VITAL clinical trial on vitamin D and omega-3 supplements; we reported on its initial findings about cardiovascular disease and cancer in December 2018. Results for many other endpoints—including physical disability, falls, and fractures—will be published in the next year or two. Because VITAL was longer (five years), larger (nearly 13,000 people took vitamin D), and used higher doses (2,000 IU a day), it may provide more definitive answers.
This article first appeared in the UC Berkeley Wellness Letter.
Also see The Best Ways to Prevent Falls.